Semiconductor devices have been pushed to smaller and smaller sizes. Different patterning techniques have been developed to allow for these smaller sizes. These techniques include spacer defined quadruple patterning, extreme ultraviolet lithography (EUV), and Spacer Defined Double patterning. These approaches have allowed production of sub-25 nm resolution patterns on semiconductor devices.
Directed self-assembly (DSA) has been considered as an option for future lithography applications. DSA may involve the use of block copolymers to define patterns for self-assembly. The block copolymers may include poly(methyl methacrylate) (PMMA), or polystyrene (PS), such as for example poly(styrene-block-methyl methacrylate) (PS-b-PMMA). Other block copolymers may include emerging “high-Chi” polymers, which may potentially enable small dimensions.
Block copolymers may phase separate under certain conditions to form periodic nanostructures, as in PS-b-PMMA. Phase separation is a situation similar to that of oil and water. Oil and water are immiscible because they phase separate. Due to incompatibility between the blocks, block copolymers may undergo phase separation. Because the incompatible blocks are covalently bonded to each other, they cannot separate macroscopically. During “phase separation” the blocks form nanometer-sized structures in which the incompatible blocks are separated maximally while still being covalently bonded to each other, while the compatible blocks may group maximally together by finding similar neighboring blocks. Depending on the relative lengths of each block, several structures may be obtained.
DSA may be used, for example to form parallel lines and spaces structures or regular arrays of holes with very small pitch and critical dimensions. In particular, DSA can define sub-25 nm resolution patterns through self-assembly, while guided by surface topography and/or surface chemical patterning.
A drawback of DSA may be that the obtained structure of parallel lines or array of holes may have some defects at random locations. The defects may be caused by a not sufficient phase separation (e.g. self-assembly) in the anneal step.
For an array of lines the defects may be defined, for example, by bridges when two parallel lines which are perfectly phase separated both are interrupted at the same location by a not phase separated area (bridge) or further by a dislocation where the parallel configurations of the lines is distorted at a certain location.